Methods and systems for multi-tuned cab signal pickup coils

ABSTRACT

Methods and systems for a cab signal pickup coil assembly are provided. The system includes an assembly including at least one elongate magnetic core and a plurality of pickup coils concentrically spaced about the magnetic core wherein the pickup coils are configured to be responsive to a magnetic field in the magnetic core. The pickup coils are grouped in sets of pickup coils along an axial length of the magnetic core. At least two sets of pickup coils are at least partially tuned using respective tuning capacitors to be responsive to different respective cab signal carrier frequencies.

BACKGROUND OF THE INVENTION

This invention relates generally to methods and systems for detecting coded or modulated electrical currents that are transmitted through the rails of a railroad track for control purposes and, more particularly, to cab signal systems and methods that are interoperable across two or more cab signal territories having different carrier frequencies.

At least some known cab signal coil assemblies are formed from a magnetic material, such as laminated steel or ferrite, with associated windings to generate a voltage proportional to a local alternating magnetic field surrounding a railroad rail. The magnetic field includes a carrier frequency portion and a signal position. In some cases, capacitors are added to the magnetic circuit to provide tuning or selective carrier frequency sensitivity. Tuning cab signal pickup coils increases the gain of the circuit as well as rejects out-of-band frequency, simplifying system design. However, current pickup coil assemblies are limited to a single carrier frequency, which limits their use to a single carrier frequency territory. To permit interoperable use across additional carrier frequency territories requires adding additional equipment and switching components.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a cab signal pickup coil assembly includes an assembly including at least one elongate magnetic core and a plurality of pickup coils concentrically spaced about the magnetic core wherein the pickup coils are configured to be responsive to an alternating magnetic field in the magnetic core. The pickup coils are grouped in sets of pickup coils along an axial length of the magnetic core. At least two sets of pickup coils are at least partially tuned using respective tuning capacitors to be responsive to different respective cab signal carrier frequencies.

In another embodiment, a cab signal system includes a receiver configured to be mounted on board a locomotive, and at least one pickup coil assembly communicatively coupled to the receiver. The at least one pickup coil assembly is configured to sense an alternating magnetic field around a rail of a railroad track produced by control information transmitted through the rail wherein the control information is transmitted using a plurality of carrier frequencies. The at least one pickup coil assembly includes sets of pick up coils wherein each set is tuned to one of the plurality of carrier frequencies.

In still another embodiment, a method of receiving a railway cab signal on board a railway vehicle includes receiving control information transmitted through railroad rails to a signal coil assembly mounted on board the railway vehicle using a carrier having a frequency in a first predetermined range, and receiving control information transmitted through railroad rails to the signal coil assembly using a carrier having a frequency in a second predetermined range wherein the first and second predetermined ranges are different and wherein the first and second predetermined ranges are selected based on a magnetic interaction of coils within the signal coil assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a cab signal system in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view of the pickup coil assembly shown in FIG. 1 in relation to a railroad rail; and

FIG. 3 is a graph of a response of pickup coil assembly in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

FIG. 1 is a schematic block diagram of a cab signal system 100 in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, cab signal system 100 includes an inductive track receiver such as a pickup coil assembly 102 converts a magnetic field vector (not shown in FIG. 1) received along a longitudinal axis 104 into a cab signal 106 which is supplied to a cab signal receiver 108 for processing. Cab signal receiver 108 extracts data from cab signal 106 and supplies the extracted data to an operator display 110. In an alternative embodiment, data extracted from cab signal 106 may be transmitted to other onboard systems 112 or off board systems through a wireless communication link 114.

FIG. 2 is a cross-sectional view of pickup coil assembly (shown in FIG. 1) in relation to a railroad rail 202. In the exemplary embodiment, pickup coil assembly includes a housing 204 enclosing an elongate magnetic core 206 formed of a highly permeable material such as, for example, but not limited to, ferrite or laminations of iron or steel. One or more pick-up coils 208 are concentrically arranged about core 206 and are magnetically coupled to core 206 such that an alternating flux flowing in core 206 tends to generate a signal in pick-up coils 208. Sets 210 of pick-up coils 208 are spaced along core 206 to facilitate a magnetic independence between adjacent sets 210 of pick-up coils 208. Such spacing comprises a gap 218 between adjacent sets 210. In an alternative embodiment, there is no intentional gap between adjacent sets 210. In the exemplary embodiment, a first set of pick-up coils 208 includes approximately nine individual pick-up coils 208 tuned to a specific cab signal frequency via capacitor 220 and a second set of pick-up coils 208 includes a single pick-up coil 208 tuned to a different cab signal frequency via capacitor 221. In an alternative embodiment, any number of pick-up coils 208 may be grouped together to determine a tuning of pickup coil assembly to predetermined carrier frequencies.

During operation, a cab signal carrier transmitted in one rail 202 in a first direction, shown by the cross (+) in rail 202 travels through the wheels and axle of a railway vehicle (not shown) and returns to its source in an opposite direction in the other rail (not shown). Because the carrier signal is an AC signal, on a next half-cycle the cab signal is transmitted in an opposite direction in rail 202. The current flowing in rail 202 generates a magnetic field vector 212 around rail 202 in a direction 214. Magnetic field vector 212 extends circumferentially outward from rail 202 and intersects core 206, which is positioned orthogonally with respect to rail 202 a height 216 from rail 202. Each pick-up coil 208 surrounding core 206 interacts with the alternating magnetic field flowing through core 206 and with a magnetic field generated in each other adjacent pick-up coil 208. Varying the capacitance of tuning capacitor 220 and/or 221 varies the response of respective sets 210 of pick-up coils 208. In one embodiment, the capacitance of tuning capacitor 220 and/or 221 is switchable, variable, or digitally variable. An arrow superimposed on a conventional diagram of a capacitor component represents a variable capacitance. In the exemplary embodiment, capacitor 220 and/or 221 may comprise a varactor or an electrically controlled variable capacitor. In the exemplary embodiment, a set of nine pick-up coils 208 is tuned to be responsive to a carrier frequency of approximately 100 Hertz. A second set 210 of pick-up coils 208 includes a single pick-up coil 208 and is tuned to be responsive to a carrier frequency of approximately 2050 Hertz. In the exemplary embodiment, to enhance magnetic independence in coil sets, a gap 218 is placed between coil sets. A gap 218 between sets 210 of pick-up coils 208 facilitates increasing the output of the pickup coil assembly when tuning pickup coil assembly to more than a single carrier frequency. In an alternative embodiment, gap 218 is not required and no intention gap is formed between sets of coils.

FIG. 3 is a graph 300 of a response of pickup coil assembly 102 in accordance with an exemplary embodiment of the present invention. Graph 300 includes an x-axis 302 graduated in units of frequency and a y-axis 304 graduated in units of volts/amps at a predetermined coil height 216 above rail 202. A trace 306 indicates a response of pickup coil assembly 102 to a cab signal transmitted through a rail at various frequencies. In the exemplary embodiment, pickup coil assembly 102 is tuned to a frequency of approximately 100 Hz and a frequency of approximately 2050 Hz using sets of pickup coils 208. Trace 306 includes a first local peak 308 at approximately 100 Hz and a second local peak 310 at approximately 2050 Hz. Rapid fall off of the cab signal above and below the tuned frequencies permits cab signal system 100 to readily distinguish the cab signal from noise which may be present in the rail. The individual peaks 308 and 310 at separate carrier frequencies permits a single pickup coil assembly 102 to be interoperable across different carrier frequency territories without additional components or a need to switch between separate coil assemblies.

Although system 100 has been illustrated with a pickup coil assembly 102 tuned to receive only two separate carrier frequency ranges, it should be understood that any number of different carrier frequency ranges can be accommodated using the methods and systems described herein.

The above-described methods and systems for providing cab signal pickup assemblies that are interoperable across two or more cab signal territories having different carrier frequencies. The system provides a single cab signal pickup coil that is capable of being tuned to two or more frequencies that is cost-effective and highly reliable.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

1. A cab signal pickup coil assembly comprising: at least one elongate magnetic core; and a plurality of pickup coils concentrically spaced about said magnetic core, said pickup coils configured to be responsive to an alternating magnetic field in said magnetic core, said pickup coils grouped in sets of pickup coils along an axial length of said magnetic core, at least two sets of pickup coils at least partially tuned by respective tuning capacitors to be responsive to different respective cab signal carrier frequencies.
 2. A system in accordance with claim 1 wherein said magnetic core comprises a longitudinal axis, said magnetic core is configured to be positioned proximate a rail such that a longitudinal axis of the rail is substantially orthogonal with respect to the longitudinal axis of the magnetic core.
 3. A system in accordance with claim 1 wherein ones of said sets of pickup coils are separated from an adjacent set of pickup coils by an air gap.
 4. A system in accordance with claim 1 wherein said tuning capacitors comprise an electrically controlled variable capacitor.
 5. A system in accordance with claim 1 wherein the capacitance of the tuning capacitors is at least one of switchable, variable, and digitally variable such that a frequency response of the sets of pick up coils is variable.
 6. A system in accordance with claim 1 wherein sets of pickup coils are separated from adjacent sets of pickup coils by a material having a predetermined reluctance.
 7. A system in accordance with claim 1 wherein pick up coils in a set are electrically coupled in series.
 8. A system in accordance with claim 1 wherein at least one set of pickup coils reduces noise above and below a first cab signal carrier frequency and has a center frequency between about 40 Hz and about 250 Hz.
 9. A system in accordance with claim 1 wherein at least one set of pickup coils reduces noise above and below a first cab signal carrier frequency and has a center frequency of about 100 Hz.
 10. A system in accordance with claim 1 wherein at least one set of pickup coils reduces noise above and below a second cab signal carrier frequency and has a center frequency between about 1500 Hz and about 4550 Hz.
 11. A system in accordance with claim 1 wherein at least one set of pickup coils reduces noise above and below a first cab signal carrier frequency and has a center frequency of about 2050 Hz.
 12. A cab signal system comprising: a receiver configured to be mounted on board a locomotive; at least one pickup coil assembly communicatively coupled to said receiver, said at least one pickup coil assembly configured to sense an alternating magnetic field around a rail of a railroad track produced by control information transmitted through the rail wherein the control information is transmitted using a plurality of carrier frequencies, said at least one pickup coil assembly comprising sets of pick up coils each tuned to one of the plurality of carrier frequencies.
 13. A system in accordance with claim 12 further comprising a pickup coil assembly mount configured to couple said pickup coil assembly to a locomotive such that a longitudinal axis of said pickup coil assembly is substantially orthogonal with respect to the track.
 14. A system in accordance with claim 12 wherein said at least one pickup coil assembly comprises: an elongate core; and at least one pickup coil concentrically mounted around said elongate core.
 15. A system in accordance with claim 12 wherein said tuning capacitor is external to said pickup coil assembly
 16. A system in accordance with claim 12 wherein said at least one pickup coil assembly comprises a coil wound with a plurality of adjacent turns concentrated axially along an elongate core and a tuning capacitor coupled electrically in parallel.
 17. A method of receiving a railway cab signal on board a railway vehicle comprises: receiving control information transmitted through railroad rails to a signal coil assembly mounted on board the railway vehicle using a carrier having a frequency in a first predetermined range; and receiving control information transmitted through railroad rails to the signal coil assembly using a carrier having a frequency in a second predetermined range, wherein the first and second predetermined ranges are different, the first and second predetermined frequency ranges selected based on a tuning of coils within the signal coil assembly.
 18. A method in accordance with claim 17 further comprising traversing from a first locale where cab signals are transmitted using a carrier having a frequency in a first predetermined range predominate to a second locale where cab signals are transmitted using a carrier having a frequency in a second predetermined range predominate.
 19. A method in accordance with claim 17 further comprising mounting a signal coil assembly to the railway vehicle such that a longitudinal axis of the signal coil assembly is maintained substantially orthogonal with respect to the rail.
 20. A method in accordance with claim 17 further comprising positioning a plurality of pickup coils concentrically spaced about a signal coil assembly magnetic core wherein the pickup coils are configured to be responsive to an alternating magnetic field in the magnetic core, the pickup coils being grouped in sets of pickup coils along the magnetic core wherein at least two sets of pickup coils are at least partially tuned using a respective tuning capacitor to be responsive to different respective cab signal carrier frequencies. 